Simultaneous transmission and reception on the same carrier, i.e. the FD transmission on the same carrier, has been known to be possible in theory, but it has been earlier deemed to be an unfeasible concept for mobile communications in practice because a transmission signal of a mobile phone ‘leaks’ into the receiver of the mobile phone. This is termed self-interference. The self-interference is difficult to remove in practice. However, some researchers in Standford University and Rice University have recently developed a practical full duplex system by using combined and advanced self-interference cancellation schemes. The FD transmission can easily double data throughput in a wireless communications system and if the FD transmission is cleverly implemented on Medium Access Control (MAC) layer of the wireless communications system, the data throughput may be even higher.
In current wireless networks, such as an LTE network, communications is based on Half-Duplex (HD) transmission. Thus, simultaneous data transmission and reception using the same time slot and frequency is not allowed. Even if base stations of the LTE network, i.e. eNBs, are capable of FD, the most UEs are likely HD devises and thus incapable for full dublex transmissions. One known solution to utilize the FD capability in an eNB of the network is as follows. The eNB or base station (BS) defines two UE groups: “UE group #1” and “UE group #2” so that UL/DL subframes of different groups are not overlapped, wherein the UL subframes are included in one group's frame where the DL subframes are included in the other group. When the eNB detects an UE, it places the UE into one of the two groups. By doing this, each Half-Dublex (HD) UE will operate as a normal Time Division Dublex (TDD) UE and the full duplex transmission is realized in the eNB side only.
FIG. 1 illustrates non-overlapping UL/DL subframes of different UE groups. There are two UE groups, Group #1 and Group #2, and the both UE groups include one or more UEs. The eNB has allocated seven subframes 101-107 to Group #01 and seven subframes 108-114 to Group #02. When time passes, the UEs of Group #1 uses the subframes 101-107 from left to right, and simultaneously the UEs of Group #2 uses the subframes 108-114. Each subframe 101-114 includes a letter disclosing to which type of use each subframe is intended for. The letter U means an uplink transmission, the letter D means a downlink transmission, and the letter S means “special frame”. As can be seen in the figure, in the all simultaneous pairs of subframes (101 & 103, 102 & 104, etc.) the uplink transmissions are non-overlapping in time and also the downlink transmissions are non-overlapping.
The solution of FIG. 1 works fine, if the UEs are placed in appropriate way into groups and the UEs stay where they are. In practice, when the UEs are mobile devices at least some UEs move. Two UEs belonging to different groups may come close to each other, because at least one of them has moved and the distance between them is shortened. Sometimes the UEs are originally placed into the groups so that the distance between them is too short, i.e. the grouping is non-optimal. Due to the mobility of the UEs or the non-optimal grouping, two UEs belonging to different groups may be close to each other while performing transmission and cause serious transmission interferences to each other. This is one of the problems which the present invention aims to solve.